Field of the Invention
The present invention relates to a member of CaF2 polycrystalline body with excellent corrosion durability.
Background
CaF2 single crystal has a high transmittance characteristic of light ranging from ultraviolet region to infrared region and is used as a lens material. CaF2 has lower deliquescent properties and is a more stable fluoride compared with MgF2 and BaF2 fluorides.
In addition, CaF2 has also excellent durability such as fluorine-plasma durability, HF (hydrogen fluoride) durability, chemical durability, and heat durability and therefore CaF2 is available as a plasma-durable member or a crucible member.
However, CaF2 single crystal has cleavability and therefore can be easily cracked by vibration or impact.
In contrast, CaF2 polycrystalline body is superior in that it does not have cleavability as a bulk material because microscopic crystals are bound together to constitute CaF2 polycrystalline body.
On the other hand, it is known that polycrystalline body generally has a grain boundary and the grain boundary surface is preferentially corroded and etched. Therefore, a single crystal which does not have the grain boundary surface is superior from the viewpoint of corrosion durability. Thus, there is a need for a CaF2 member which is poly crystal and yet has improved corrosion durability.
Moreover, superior process-ability is required in order to use as a member.
In order to meet such a need, a member for a semiconductor manufacture apparatus is proposed which is constituted of a high-density fluoride sintered body of which a relative density is 95% or more and an average grain size of crystalline grains is 30 μm or less (for example, refer to Japanese Patent Publication No. 3618048).